This invention relates to the art of electrically sensing physical contact between two relatively movable conductive elements, and more particularly to a new and improved method and apparatus for detecting the point of contact between a conductive workpiece and a relatively movable conductive element such as an electrode insulated from the workpiece.
One area of use of the present invention is for determining the point of contact between the workpiece and electrode of an electrical discharge machine, although the principles of the present invention can be variously applied. The point of contact between the workpiece and electrode in an electrical discharge machine must be very critically determined in order to achieve the desired workpiece accuracy. However, problems such as transient contact, varying gap geometry, dielectric gap contamination, etc. associated with determining such accuracy of contact have not been solved by the prior art. A related illustration of such problems in ascertaining accuracy of contact involved the use of "whisker" electrodes to drill very small diameter holes in a workpiece and the fact that an oil drop on the workpiece can exert sufficient force on the electrode to cause that electrode to deflect and thereby give a false reading of the contact position.